The culprit was intestinal stasis, leading to that horror of horrors, autointoxication. It was, please pardon the term, constipation.

It was universal. Astute doctors could spot victims everywhere, even on city streets, by their telltale greasy skins and septic open mouths. Autointoxication meant that toxins from backed-up, rotting wastes were seeping into their bloodstreams, poisoning their bodies and minds.

They needed help. They needed cleaning out. They needed laxatives, roughage, special exercises, trusses, gut-pounding massages, abdominal vibrating machines and a menacing array of equipment to administer "internal baths" and restore muscle tone to their flaccid innards. Sometimes, they needed drastic surgery to rearrange their insides.

This obsession with the bowels was more than a mad moment in the history of medicine. It went on for a century or more, and it is not over yet, according to a book published in March, "Inner Hygiene" (Oxford University Press), by Dr. James C. Whorton of the University of Washington in Seattle. The book is exhaustive and scholarly, but, thank goodness, it is also a wry chronicle.

To anyone who grew up puzzling over delicately worded radio ads for peculiar products like Serutan ("nature's spelled backwards"), Sal Hepatica and Carter's Little Liver Pills, or wondering how Grandma could have become addicted to Feen-a- Mint laxative chewing gum, Whorton's book will explain it all.

There is no denying that constipation causes a great deal of suffering and can be serious, especially among the elderly or chronically ill. But the notion that it is the root of every illness is nonsense. The idea, however, had been around for centuries, and it was truly embraced by doctors and the public in the United States and Europe in the 1800s. It kept its hold on medicine until well into the 20th century.

By Whorton's account, a giant in the fight against constipation was the London surgeon Dr. William Arbuthnot Lane, who had his heyday during the first decade or so of the 20th century. He convinced people that virtually everyone was chronically constipated, and he made up a theory to explain it: The human digestive system had evolved in four-footed ancestors, and when people stood up on two legs, gravity was too much for their intestines, which drooped, kinked and became clogged.

Lane was a great believer in mineral oil, and he gulped it down several times a day himself and also dosed everyone around him with it, including his family, his servants and his parrot, Whorton reports.

But advanced cases were too far gone for mineral oil, and Lane, who was said to be a brilliant surgeon, devised ever bolder and more useless operations, taking out more and more of people's intestines to relieve them of kinks and blockages.

Most of his patients were women, some of whom married after the surgery. Lane took the credit, claiming that no one would have married them before he straightened out their knotted guts, improving both their looks and their dispositions.

By the 1920s, Lane's theories and operations had been discredited and even ridiculed by his colleagues, one of whom pointed out that by his gravitational theory, penguins, gorillas and especially bats, since they hang upside down, should suffer terribly from constipation.

But the cult of the colon still ruled, and gave rise during the 1920s to a laxative industry and volumes such as "Intestinal Management for Longer, Happier Life." No matter that doctors said anything from three times a day to once every three days was normal, there was money to be made by convincing people of the great peril of "irregularity."

An American ad during that era warned that poisonous gases would spread through the body unless "bowel bloat" was cleaned out gently but thoroughly with Cascarets Candy Cathartic. Other ads claimed that laxatives were a great way to lose weight, and Ex-Lax called itself "the secret of natural beauty." Food crazes for bran, yeast, yogurt and sour milk to prevent constipation also sprang up during the 1920s, and Battle Creek, Mich., home of Kellogg's All Bran and Post Grape Nuts, became the cereal capital of the world, marketing products to promote regularity.

All of this might seem like a quaint and amusing chapter in the history of weird medical beliefs. But is it history?

Given Americans' current preoccupation with high-fiber diets, and their endless parental fussing over the contents of children's diapers, one could easily argue that old fears of autointoxication must still be with us. As late as 1986, the National Institutes of Health was still writing pamphlets to reassure the public that the human body did not absorb poisons from retained feces.

Today, herbal and alternative medicine magazines carry ads for "cleansing programs" that promise to rid the body of toxins that linger in the intestines in a slimy layer of something called "mucoid plaque." Americans still spend $600 million a year on laxatives.